Ten South Korean kindergartners were killed in a traffic accident in China on Tuesday, after a bus they were in caught fire, Seoul’s Foreign Ministry said.

The accident took place at around 9 a.m. in Weihai, Shandong province, as the vehicle crashed into a garbage truck in front of them, catching fire while in a tunnel.

Twelve people aboard died, including a Chinese child and the Chinese bus driver, while a Chinese instructor was severely injured, the ministry said.

“We have dispatched eight officials from the consulate-general in Qingdao, including its chief, and are looking into further details of the accident,” the ministry said in a statement, noting that the Weihai police were carrying out DNA tests to identify the victims.

Yonhap News Agency reported that the high number of casualties could be attributed to the door of the bus that could not be opened, citing a tip. Video footage purportedly taken by an eyewitness shows the door side of the burning bus obstructed by the tunnel wall.

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Shortly after the crash, then acting President and Prime Minister Hwang Kyo-ahn expressed “deep regret,” instructing the foreign and justice ministries to make the utmost efforts to handle the aftermath and assist the bereaved families residing there.

Meanwhile, criticism is rising in China after allegations surfaced that no other motorists offered to help, with some even taking pictures of the burning bus before driving from the scene.

Online news media outlet Phoenix reported video clips showed the tunnel filled with smoke and the bus left in a blaze, while other cars passed by. Multiple fire trucks were also seen struggling to get into the tunnel.

Yonhap News Agency also said the trucks took more than 10 minutes to arrive and begin fighting the fire, citing Chinese police authorities, embassy officials and witness testimony. The blaze was extinguished some 27 minutes after the accident, it said, adding at least a few more lives may have been saved if others helped to open the door from outside.